Event Service Cautions

The Exchange Event Service fires events asynchronously rather than synchronously in the context of the Exchange Information Store, so the Information Store won't block your event script or other processes or people from working on the items in the folder if your script hasn't run yet. A user or another process, then, could delete, move, or change an item before an event based on the item is fired and your script is executed. Your scripts will receive the proper events in this situation, but the items might not be available. For this reason, don't use the Event Service to monitor folders, such as your Inbox and Outbox, that have very high volumes of items entering, leaving, or being deleted. In these types of folders, the chances are greater that the user or the rules engine on the server will move or delete the item before your script is run.

You shouldn't use the Event Service to provide a mechanism for "house rules" either. House rules are general rules containing business logic that you want installed on every folder in the system. Using the Event Service for a system that uses house rules will bog down the Exchange Servers running the Event Service because of the high volume of messages generating events. As well, you would have to manually install the agent in every folder because the Event Service does not provide this capability. The Agent Install application discussed later in this chapter will help you get around the problem of manually installing scripts into folders. The Agent Install program will show you how to programmatically create and bind agents using the components that ship with the Exchange Event Service.